So you’ve got a PostgreSQL instance (maybe locally, maybe in Kubernetes, or it could be a cloud service like RDS or Timescale), and you’re ready t

5 Common Connection Errors in PostgreSQL and How to Solve Them

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2024-04-25 13:30:05

So you’ve got a PostgreSQL instance (maybe locally, maybe in Kubernetes, or it could be a cloud service like RDS or Timescale), and you’re ready to go. You fire up psql to start running queries… but your connection doesn’t work. This post examines the five most common connection errors in PostgreSQL and how you can solve them.

This message is a classic, usually followed up with “remaining connection slots are reserved for non-replication superuser connections.”

PostgreSQL has a limited number of connections to the database, controlled by the max_connections parameter. This could be set globally, on a role, or in a database. When you exceed this number, new connections will get this error, although superusers may still be able to connect (another parameter controls the limit for them, max_superuser_connections).

💡 Solution: You need to reduce your connection counts in the short term. Either stop some applications that are connected to the database, log in a superuser, and terminate some of the connections, or, as a last resort, restart the PostgreSQL service to dump all connections (but you’d also lose all open transactions).